SWOG S1929: Phase II randomized study of maintenance atezolizumab (A) versus atezolizumab + talazoparib (AT) in patients with SLFN11 positive extensive stage small cell lung cancer (ES-SCLC).
Authors: Nagla Fawzy Abdel Karim, Jieling Miao, Karen L. Reckamp, Carl Michael Gay, Lauren Averett Byers, Yingqi Zhao, Mary Weber Redman, Daniel R. Carrizosa, Wei-Lien Wang, William J. Petty, Kathan Mehta, Bryan A. Faller, Edem S. Agamah, Samer S. Kasbari, Rajini Katipamula Malisetti, Atul Kumar, John Schallenkamp, Krishna Chaitanya Alluri, Jhanelle Elaine Gray, Karen Kelly
Journal: Journal of Clinical Oncology (2023)

8504 Background: In unselected patients (pts) with extensive-stage small cell lung cancer (ES-SCLC), the addition of immune checkpoint inhibitors (ICI) to chemotherapy resulted in a modest improvement in OS. In a retrospective analysis of a study with veliparib (PARP inhibitor [PARPi]) and temozolomide in patients with SCLC, Schlafen-11 (SLFN11) predicted PFS and OS benefit for the addition of PARPi. We evaluated whether the addition of PARPi (talazoparib) to standard-of-care maintenance ICI (atezolizumab) following frontline chemoimmunotherapy improved outcomes in pts with SLFN11-positive ES-SCLC. Methods: Participants with ES-SCLC expressing SLFN11 (H-score ≥ 1, evaluated centrally at MDACC) were randomized to maintenance atezolizumab (A) versus atezolizumab plus talazoparib (AT) following frontline chemotherapy and A. Randomization was stratified by Zebrod PS (0-1 vs 2) and use of consolidation thoracic radiation. The primary endpoint was PFS, and secondary endpoints included ORR, OS, and toxicity. The primary analysis was done using a 1-sided 10% level stratified log-rank test. Target sample size was 94 pts. Results: From June 2020 to December 2022, 309 pts were screened, of which 204 of 259 (79%) with evaluable tissue were SLFN11 positive, and 106 were randomized (52 A, 54 AT). Median follow up time is 5 months. Median age was 67 (45-84); 51 (48%) were females; 94 (89%) were white,102 (96%) were PS 0-1, and 26 (25%) had radiation prior to randomization. With 80 PFS events reported, PFS was significantly improved with AT (hazard ratio [80% CI]: 0.70 [0.52-0.94]; p = 0.056). Median PFS was 2.8 months (80% CI 2.0-2.9) for A and 4.2 months (80% CI 2.8-4.7) for AT. OS was not different (hazard ratio [80% CI]: 1.17 [0.80-1.71]; p = 0.30). Median OS was 8.5 months (80 % CI 7.4-12.7) for A and 9.4 months (80% CI 8.1-14.2) for AT. ORR was 16% (5/32, 80% CI 8-27%) for A and 12% (4/34, 80% CI 5-22%) for AT. Grade 3 or greater treatment related non-hematological adverse events (AEs) occurred in 13% pts in A and 15% in AT. Hematological AEs occurred 4% in A compared to 50% pts in AT (Expected for T) (p &lt; 0.001). There were no treatment related grade 5 events. One participant on AT experienced grade 3 febrile neutropenia. The majority of grade 3 AEs were due to anemia (2% in A and 37% in AT). Only three pts discontinued treatment due to toxicity (2 in A and 1 in AT). Conclusions: This study met its primary endpoint demonstrating that maintenance AT improved PFS in SLFN11-selected patients with ES-SCLC. Hematologic toxicity was increased with AT as expected, with majority being grade 3 anemia. This study demonstrates the feasibility of conducting biomarker selected trials in SCLC, paving the way for future evaluation of novel therapies in selected SCLC populations. Clinical trial information: NCT04334941 .